4.7 cm long insect is perpendicular to the optical axis of a thin lens; the bug

Question

4.7 cm long insect is perpendicular to the optical axis of a thin lens; the bug is 6.4 cm away from the lens. The lens forms an inverted image of the insect which is 0.8 cm long on a screen behind the lens. (Use three significant figures.)

a. How far behind the lens is the screen? ______________cm

b. What is the lens' focal length (pay attention to sign)?__________________ cm

c. If the insect were instead only 0.22 cm from the lens, what would the image distance be (pay attention to sign)? _________________cm

d. Could the new image be projected on a screen?

yes OR no OR possibly

Explanation / Answer

hi/ho = 0.8/4.7 = 0.17 = s'/s

a) s' = 0.17*s = 1.088 cm

b) 1/s + 1/s' = 1/f

1/6.4 + 1/1.088 = 1/f

f = +0.93 cm cm

c) 1/s + 1/s' = 1/f

1/0.22 + 1/s' = 1/0.93

s' = -0.288 cm

d) s' = negative it is a virtual image

so image cannot be projected.............NO

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